Photographic colloid transfer process



United States Patent 3,232,757 PHUTGGRAPHIC COLLOID TRANSFER PROCESS Joseph T. Leone, Rochester, N.Y., assignor to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed Dec. 17, 1962, Ser. No. 244,899 2 Claims. (Cl. 9628) This invention relates to a process in photography wherein an image in soft adhesive organic colloid is formed photographicallyand a discrete stratum of the image is transferred to a receiving sheet to provide a reproduction of the subject.

The colloid transfer process is described in the Yutzy et al. US. Patents 2,596,756, granted May 3, 1952, and 2,716,059, granted August 23, 1955, and embodies the exposure to a subject of a substantially unhardened gelatino-silver halide emulsion layer which may contain a gelatin tanning silver halide developing agent as well as a non-tanning silver halide developing agent. Upon activation of the exposed emulsion with an alkaline solution in the presence of the developing agent or agents, tanning development of the more exposed regions of the emulsion corresponding to the highlights of the subject proceeds although some development of the less exposed regions also takes place to provide visual density for the transferred image as explained in more detail in U.S. Patent 2,716,- 059 above. Thereafter the developed emulsion is pressed into contact with an absorbent receiving sheet such as paper to cause the less exposed regions, and thus the less developed regions, of the emulsion to adhere to the receiving sheet. Subsequently, when the emulsion and receiving sheet are separated, a stratum of the less exposed regions of the emulsion remains on the sheet and appears as a positive silver image of the original subject.

As mentioned in the above patents, the alkaline solution used for activation of the exposed emulsion layer advantageously contains a gelatin-softening agent to facilitate transfer of the less exposed portions of the emulsion to the receiving sheet. Urea and certain other gelatinsoftening agents have been suggested for the purpose. The above patents also suggest the use of sodium carbonate as the alkaline component of the alkaline solution used for initiating development of the exposed emulsion.

I have discovered that in the described process a distinct advantage resides in rep-lacing urea and sodium carbonate by a mixture of guanidine carbonate and potassium carbonate as the gelatin-softening and alkaline component in the mentioned solution. That is, the solution of urea and sodium carbonate has the undesirable property of readily crystallizing out on processing equipment used in commercial installations and eventually rendering movable parts, particularly of continuous processing equipment, difficult or impossible to operate. Thus a squeegee blade or roller designed to press the sensitive element against the reception sheet in the transfer step may not impart the proper pressure and a print of inferior quality results. Also, an accumulation of chemical dust resulting from the crystallization of the compounds on the equipment and adjacent surfaces may have an adverse effect on the photosensitive emulsion.

When the combination of guanidine carbonate and potassium carbonate is used in the alkaline solution these troubles are substantially eliminated. The solution does not readily crystallize out on the processing equipment, particularly since concentrated solutions of the compounds are liquid at much lower relative humidities.

One object of this invention is to provide an improved activator for the colloid transfer process that can be supplied in concentrated liquid form. A further object of this invention is to provide an activator solution which "ice has a higher tolerance for evaporation of water from the activator solution. An additional object of this invention is to provide .an activator solution which may be stored in concentrated liquid form for extensive periods of time Without deteriorating. V

A useful operating range of the activator ingredients varies between about 1.3% to2.6% for guanidine carbonate and about 23.5% for potassium carbonate. Preferably, the total carbonate concentration should not be greater than 4% when all of the carbonate is determined as potassium carbonate.

The useful concentration ratios of guanidine carbonate to potassium carbonate can be varied between about 1 to 5.5 and 1 to 0.75. Any formulation falling within these limits exhibits marked improvement in evaporation tolerance and the number of good copies produced when compared to known activators. The higher the ratio -of guanidine carbonate to potassium carbonate Within these limits, the better the evaporation tolerance of the activator.

The following examples will serve to illustrate my invention.

Example 1 A substantially unhardened gelatino-silver halide emulsion (having a hardness as defined in the above patents) is prepared as described in U.S. Patent 2,716,059 above and containing a mixture of tanning and substantially non-.

tanning silver halide developing agents such as 4-phenylcatechol and 4-methoxy-a-naphthol. The emulsion is coated on a paper supportand dried. The resultant sensitive element is then exposed to a two-tone subject (a line or halftone subject) if desired by reflex methods, and placed in the following" alkaline'solution of the inventi on to initiate development.

Percent by weight Potassium carbonate (anhyd) 4.0 Urea 2.0 Water 94.0

When hard waters are used in making up the above. solution, in order to prevent the formation of scale on equipment it is advisable to add a water softening agent such as well known alkaline earth metal chelating agents, e.g., ethylenediaminetetraacetic acid, di-, tri-, or tetrasodium salts (Sequestrene). About 4 grams of the salts are useful in the above formula for this purpose.

While development in the above alkaline solution is proceeding, light should be excluded to the extent required by the particular silver halide present in the emulsion. With daylight working emulsions limited exposure to room lights may be given during the exposure and development steps. Other emulsions may require the use of the usual safelights during the exposure and processing steps. When the proper amount of exposure has been given, gelatin tanning silver halide development occurs principally in the more highly exposed areas of the emulsion and little or no tanning development in the other areas. When development is complete as determined by trial with the particular emulsion and conditions of operation in use, the sensitive element is pressed into contact with an absorbent sheet, such as paper, by means of a squeegee blade or rollers. Immediately thereafter the sensitive element and receiving sheet are separated leaving a stratum of the less exposed and thus less hardened regions of the emulsion adhered to the receiving sheet. The result is a positive line or half-tone silver-containing image afiixed to the sheet. If desired, the transfer operation may be repeated a number of times by merely rewetting the sensitive element in the alkaline solution and squeegeeing to a fresh reception sheet. This formulation has the disadvantage of developing sludge after several matrices have been run through the activator. The activator has the added disadvantage that it cannot be packaged as a concentrate Example 2 The following formulation omitting urea was used as described in Example 1.

Percent by weight Guanidine carbonate 0.65 Potassium carbonate 3.5 Sequestrene- 4Na 0.5

Example 3 The following formulation was used as in Example 1.

Percentby weight Guanidine carbonate 1.3 Potassium carbonate 3.0 Sequestrene 4Na 0.5

The results were like those of Example 2, except that the evaporation tolerance of liquid loss in the activator solution can be increased up to 45% and still activate matrices so as to obtain good transfer copies.

Example 4 The following formulation was used as in Example 1. Percent by weight Guanidine carbonate 2.6 Potassium carbonate 2.0 Sequestrene 4Na 0.5

The resultswere like those of Example 2 except that the evaporation tolerance of. the. liquid loss in the activator solution can be increased to over 50% and still activate matrices so as to obtain good transfer copies.

As can be seen from the above examples, the increase in the ratio of guanidine carbonate to potassium carbonate tends to increase the evaporation tolerance of the activator solution. If this ratio is increased to above about 1 to 0.75, the activator increases the speed of the matrix development beyond the area of good time control normally useful in the operation of obtaining copies by the colloid transfer system disclosed.

In a preferred embodiment of the invention the gelatin tanning and non-tanning developing agents are present in the emulsion. However, either or both developing agents may be present in the alkaline solution and the other in the emulsion. A very useful combination of developing agents is 4-phenylcatechol with 4-methoxy-otnaphthol. Since the latter is self-coupling it forms a colored compound during development which contributes density to the print. Other useful tanning and non-tanning silver halide developing agents are disclosed by the above patents.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

I claim:

1. A method of photographic reproduction which comprises developing an exposed substantially nonhardened gelatino-silver halide emulsion layer, said emulsion being not harder than a gelatin layer containing 0.7 gram of formaldehyde per pound of gelatin freshly coated, said emulsion containing a gelatin tanning silver halide developing agent and a substantially non-tanning silver halide developing agent, with a solution of 1.3% to 2.6% by weight guanidine carbonate and 2.0 to 3.5% potassium carbonate to obtain a hardened gelatin and silver image in the areas of the emulsion layer corresponding to the highlights of the subject, and substantially unhardened gelatin, silver and silver halide in the areas of the emulsion layer corresponding to the shadows of the subject, said development being such as to prevent any substantial tanning of the emulsion layer in said areas corresponding to the shadows of the subject, pressing a sheet having an absorbent surface against said emulsion layer while said emulsion layer is moist to cause only the shadow areas of the emulsion to adhere to the sheet, and separating said sheet and emulsion layer to transfer only a stratum of said shadow areas of the emulsion layer to said sheet.

2. An alkaline activator solution for use in the colloid transfer process consisting essentially of an aqueous solution of 1.3% to 2.6% by weight guanidine carbonate and 2.0 to 3.5% by weight potassium carbonate, said activator being free of silver halide developing agents.

References Cited by the Examiner UNITED STATES PATENTS NORMAN G. TORCHIN, Primary Examiner. 

1. A METHOD OF PHOTOGRAPHIC REPRODUCTION WHICH COMPRISES DEVELOPING AN EXPOSED SUBSTANTIALLY NONHARDENED ELATINO-SILVER HALIDE EMULSION LAYER, SAID EMULSION BEING NOT HARDER THAN A GELATIN LAYER CONTAINING 0.7 GRAM OF FORMALDEHYDE PER POUND OF GELATIN FRESHLY COATED, SAID EMULSION CONTAINING A GELATIN TANNING SILVER HALIDE DEVELOPING AGENT AND A SUBSTANTIALLY NON-TANNING SILVER HALIDE DEVELOPING AGENT, WITH A SOLUTION OF 1.3% TO 2.6% BY WEIGHT GUANIDINE CARBONATE AND 2.0 TO 3.5% POTASSIUM CARBONATE TO OBTAIN A HARDENED GELATIN AND SILVER IMAGE IN THE AREAS OF THE EMULSION LAYER CORRESPONDING TO THE HIGHLIGHTS OF THE SUBJECT, AND SUBSTANTIALLY UNHARDENED GELATIN, SILVER AND SILVER HALIDE IN THE AREAS OF THE EMULSION LAYER CORRESPONDING TO THE SHADOWS OF THE SUBJECT, SAID DEVELOPMENT BEING SUCH AS TO PREVENT ANY SUBSTANTIAL TANNING OF THE EMULSION LAYER IN SAID AREAS CORRESPONDING TO THE SHADOWS OF THE SUBJECT, PRESSING A SHEET HAVING AN ABSORBENT SURFACE AGAINST SAID EMULSION LAYER WHILE SAID EMULSION LAYER IS MOIST TO CAUSE ONLY A SHADOW AREAS OF THE EMULSION TO ADHERE TO THE SHEET, AND SEPARATING SAID SHEET AND EMULSION LAYER TO TRANSFER ONLY A STRATUM OF SAID SHADOW AREAS OF THE EMULSION LAYER TO SAID SHEET. 